The present invention relates to a method for recovering fluorescent material from mercury vapour discharge lamps or the like, and to an arrangement for removing and collecting the fluorescent material.
Mercury is a necessary constituent of the fluorescent layer in mercury vapour discharge lamps. Consequently, extended or burned-out lamps must be processed in a suitable manner, so that the fluorescent material has no harmful effect on surrounding fauna and flora. Originally, expended vapour discharge lamps were dumped in the countryside at convenient dumping locations, although this procedure is now normally forbidden by the authorities. Controlled storage within the vapour discharge lamp industry has also become troublesome, due to the large quantities of waste requiring handling and supervision. In accordance with one practical method proposed some years ago the expended or scrapped lamps are crushed into fragments, coated with luminescent material, and the fragments placed in a treatment vessel in which the mercury is recovered by distillation processes. This treatment is carried out batchwise in a sealed container, into which nitrogen gas is introduced, and the container heated and placed under vacuum, such as to vapourize the mercury, the vapourized mercury being removed from the container through a bottom outlet and condensed in a cooling trap. This method is described and illustrated in Swedish Published Specification No. 7804104-3 (corresponding to U.S. Pat. No. 4,268,307). However, although the mercury is separated very efficiently, the process involved is extremely slow, taking about 9 hours to complete for each batch of 120 1, which renders the method expensive and therefore difficult to introduce in all destruction plants or in other establishments requiring to treat or process scrapped vapour discharge lamps.